1. Technical Field
The present invention is directed generally toward disk drives and, in particular, to calibrating the phase for a disk drive. Still more particularly, the present disclosure relates to a method and apparatus for calibrating phase of a write clock in a read channel in a disk drive.
2. Description of the Related Art
Some hard disk drives incorporate patterned magnetic recording media. This patterned magnetic recording media is employed to increase the amount of data that can be stored on a hard disk drive.
With patterned magnetic media, the magnetic material on the disk drive may be patterned such that islands of media are present. These islands may be isolated from other islands. These islands may be grouped into, for example, data blocks that are isolated from other data blocks. Each island is a single bit and is separated from another island by a non-magnetic region on the media. In other words, one island of data is isolated from another island in the patterned media. These different islands of media may be arranged in data tracks in which the data tracks are concentric to each other.
When writing to this type of media, the phase of a write clock may need to be aligned with the islands to avoid introducing errors and obtain the highest quality of writing data to this type of media. A calibration procedure is performed to identify the best phase for use in writing data. Further, when the media is a magnetic disk spinning in the disk drive, the internal clock of the read channel for the disk drive needs to be frequency and phase locked to the frequency and phase, respectively, of the spinning magnetic disk prior to calibrating the phase of the write clock. Still further, prior to calibrating the phase of the write clock, a time delay between the read signals and the write signals and/or an amount of separation between the read head and the write head for the disk drive needs to be determined.
Currently, the calibration of the phase of the write clock involves writing test patterns on the disk using different phases for the write clock. The calibration also may include writing a modulated phase across a predetermined phase range. With either process, the test patterns are, then, read after they have been written to the magnetic media to identify the best phase for a particular purpose. For example, a phase that allows the pattern to align most optimally with the islands of magnetic media is desirable for a write clock when writing data to patterned media.
In writing test patterns using different phases, the test pattern is written as the write clock relative to the media is varied over a complete phase cycle, and one or more test patterns are written at each phase. By repeatedly writing the test pattern at multiple phases that span a complete clock cycle, the time needed to perform this type of calibration may be greater than desired. Time is needed to allow the clock circuit to settle on a particular phase before writing the test pattern in a meaningful manner. In the case of a modulated write clock ramped phase, time is needed to allow the phase ramp to become stable. In this manner, the time it takes to access a magnetic disk to begin writing the disk depends on the time it takes to calibrate the phase of the write clock.
Therefore, it would be advantageous to have a method and apparatus which takes into account one or more of the issues discussed above, as well as possibly other issues.